Japanese Patent Disclosure No. 11-340517 discloses a semiconductor light emitting device which comprises an insulating substrate formed with wiring conductors, a semiconductor element attached on a main surface of the substrate, a reflector (a light reflecting plate) surrounding the semiconductor element on the substrate, and a light-transmittable plastic encapsulant for encapsulating the semiconductor element and reflector. FIG. 36 illustrates a known semiconductor light emitting device which comprises an insulating substrate 100, an island wiring conductor or die pad 120 and a terminal wiring conductor or bonding pad 130 formed separately from each other on a main surface 101 of insulating substrate 100, an semiconductor element or light emitting diode chip 140 secured on island wiring conductor 120, a lead wire 150 for electrically connecting an electrode on an upper surface of semiconductor element 140 and terminal wiring conductor 130, and a light-transmittable plastic encapsulant 160 for encapsulating each portion of island and terminal wiring conductors 120, 130 on main surface of insulating substrate 100, semiconductor element 140, and lead wire 150.
Island and terminal wiring conductors 120, 130 extend outwardly on main surface 101 of substrate 100, then are bent downwardly along each end surface 103, 104 and moreover are bent along a bottom surface 102 of substrate 100 to form bottom contact electrodes. Light emitted from an upper surface of diode chip 140 is irradiated to the outside through plastic encapsulant 160. The shown light emitting diode device can be surface-mounted on a circuit board with bottom surface 102 of substrate 100 in contact to the circuit board.
Light emitting diode device comprises a reflector 110 on main surface 101 of substrate 100 for surrounding diode chip 140. Substrate 100 is formed of glass fiber into a plate of the rectangular section with flat main and bottom surfaces 101, 102, and the plate is impregnated with resin. Island and terminal wiring conductors 120, 130 are formed by plating nickel and gold in turn on copper base materials attached to substrate 100 according to a printing technique. Island wiring conductor 120 comprises an island 121 formed on main surface 101 of substrate 100, an island electrode 122 extending from one end of main surface 101 of substrate 100 through end surface 103 to one end of bottom surface 102, and a narrow island wiring 123 on main surface 101 of substrate 100 for electrically connecting island 121 and island electrode 122.
Terminal wiring conductor 130 comprises a terminal 131 on main surface 101 of substrate 100, a terminal electrode 132 extending from the other end of main surface 101 of substrate 100 through end surface 104 to the other end of bottom surface 102, and a terminal wiring 133 on main surface 101 of substrate 100 for electrically connecting terminal 131 and terminal electrode 132. Terminal 131 is disposed out of a central line 108 to reduce a longitudinal length of substrate for manufacture of light emitting diode in smaller size with reflector 110 that has a ring portion 111 on main surface 101 of substrate 100.
Semiconductor light emitting element 140 is a gallium compound semiconductor such as gallium arsenic (GaAs), gallium phosphorus (GaP), gallium aluminum arsenic (GaAlAs), aluminum gallium indium phosphorus (AlGaInP), etc. A bottom electrode (not shown) of light emitting element 140 is secured substantially at the center of island 121 through an electrically conductive bonding agent. An upper electrode (not shown) of light emitting element 140 is connected to terminal 131 through lead wire 150 striding over ring portion 111 of reflector 110.
Reflector 110 has ring portion 111 and flange portions 112 provided on opposite outer sides of ring portion 111 and is formed of liquid crystal or ABS resin blended with white powder. Formed inside of ring portion 111 of reflector 110 is a reflecting surface 113 which is upwardly diverged or flaring to form a portion of conical, spheric or paraboloidal surface or similar surface thereto or combined surfaces thereof. A bottom end of reflecting surface 113 is positioned within island 121 so that light emitting element 140 is positioned within reflecting surface 113 and surrounded by ring portion 111 which is higher than light emitting element 140. Ring portion 111 is on the outer periphery of island 121, inner end of island wiring 123 and inner end of terminal 131. Flange portions 112 of reflector 110 are formed along opposite sides 105, 106 of substrate 100 and extends inwardly or widthwise to merge with ring portions 111.
Plastic encapsulant 160 comprises a pair of ramp surfaces 161, 162 which are positioned respectively inside of electrodes 124, 134, and incline respectively relative to end surfaces 103, 104 at a given angle, a pair of vertical surfaces 163, 164 which are substantially flush respectively with side surfaces of substrate 100, and a flat top surface 165 between and substantially normal to vertical surfaces 163, 164. As seen in FIG. 36, plastic encapsulant 160 covers island 121, terminal 131, each inner portion of island and terminal wirings 123, 133, reflector 110, light emitting element 140 and lead wire 150, except electrodes 124, 134, and each outer portion of islant and terminal wirings 123, 133. Each flange portion 112 of reflector 110 has a bare side surface 114 which is flush with side surface 105 or 106 and vertical surface 163 or 164 of plastic encapsulant 160.
Recent attempts have been made to adopt such semiconductor light emitting devices as light sources for traffic signals or rear lumps of automobile, and in this case, semiconductor light emitting devices must product the greater light output for people to certainly and visually observe turning on or off of the light source from an off position. To this end, new high power light emitting semiconductors have already been developed to produce a high intensity light when relatively large electric current for example more than 350 mA is supplied to the light emitting semiconductors, however, they have caused the following various problems. Specifically, when the element is activated with a large electric current over 350 mA, it is heated so that a surface of semiconductor may reach a temperature above 150° C., and therefore, plastic encapsulant is also inconveniently awfully heated by heat from the semiconductor.
As mentioned above, plastic encapsulant is formed of a light-permeable resin to transmit light from light emitting element and emit same outside. Such a resin tends to deteriorate under heat because it contains less additive amount of heat-resistible compound unlike a package for a power transistor or the like. Accordingly, in some cases, heat continuously applied from semiconductor to plastic encapsulant, reduces adhesive force of encapsulant to lead terminals or degrades environmental resistance of encapsulant so that encapsulant is separated from lead terminals to form gaps therebetween. When some foreign matter penetrates semiconductor through the gaps, the semiconductor device deteriorates the electric properties with degradation of product reliability. Furthermore, adhesive force of encapsulant is lowered too much, lead terminals are detached from encapsulant to such an extent of current breaking between semiconductor and lead terminals.
In another aspect, prior art light emitting semiconductor shown in FIG. 36 has the structure wherein lead wire 150 strides over ring portion 111 of reflector 110 to electrically connect semiconductor 140 and terminal 131. When inner diameter of reflector 110 is reduced and height of reflector 110 is increased to improve directivity of light reflected on reflector 110 and brightness (axial brightness) of light from semiconductor element 140 along an optical axis, lead wire 150 must detour along an elevated path to bond a remaining end of lead wire 150 on terminal 131 after a preceding end of lead wire 150 is bonded on semiconductor element 140. Such an arrangement is likely to cause deformation, suspension or inclination of lead wire 150 upon molding of plastic material, which may result in short circuit or breaking accident of lead wire 150. In addition, with increased height of reflector 110, a full amount of transparent resin cannot preferably be injected within reflector 110.
An object of the present invention is to provide a semiconductor light emitting device, method for producing the same and reflector for semiconductor light emitting device which has no harmful effect under heat when the light emitting device is activated with heavy current.
Another object of the present invention is to provide a semiconductor light emitting device, method for producing the same and reflector for semiconductor light emitting device which can prevent deformation of lead wire connected to a semiconductor light emitting element.
Still another object of the present invention is to provide a semiconductor light emitting device, method for producing the same and reflector for semiconductor light emitting device which can increase height of reflector to improve light directivity and axial brightness.
A further object of the present invention is to provide a method for producing a semiconductor light emitting device capable of preferably injecting and filling resin within interior of reflector in forming a plastic encapsulant.